revset: do not rewrite ':y' to '0:y' (
issue5385)
That's no longer valid since the revision 0 may be hidden. Bypass validating
the existence of '0' and filter it by spanset.
revset: extract function that creates range set from computed revisions
So we can pass m=0 to _makerangeset() even if the revision 0 is hidden.
Hidden revisions are filtered by spanset.